This invention relates to data transmission systems and is particularly, although not exclusively, concerned with systems of the kind generally referred to as local area networks.
One known form of data transmission system comprises a number of stations connected together in a ring or loop, so that data messages can be transmitted unidirectionally around the ring from one station to another. There are several ways of controlling such a ring. One known technique is to arrange for one of the stations to act as a primary station, and the others to act as secondaries. The primary can send messages on the ring at any time, whereas a secondary can send a message only if it receives a control signal, referred to as a polling signal or token, from the primary.
It has been proposed to allow the role of primary to be passed around the ring, so that each station in turn acts as the primary. One object of the present invention is to provide an improved way of passing the role of primary between stations, so as to improve the efficiency of the data transmission system.